1. Technical Field
The present invention relates in general to a method and system for data communication in a data processing system and in particular to method and system for data communication across a shared communication network in a data processing system. Still more particularly, the present invention relates to a method and system for data communication that permit devices to communicate data across a shared communication network at a selectable rate.
2. Description of the Related Art
A multiprocessor data processing system typically includes a shared system bus to which a number of processors and other devices (e.g., memory and adapters) are coupled. In such multiprocessor data processing systems, devices frequently need to communicate tasks, data, interrupts, and other information to other devices across the shared system bus. Accordingly, each device may include a bus interface unit (BIU) to manage communication across the system bus in conformance with a predetermined bus communication protocol.
Bus communication protocols for multiprocessor data processing systems are typically synchronous, that is the bus communication protocols typically require that BIU operations be performed at specified times relative to a common system clock signal. However, because of system bus loading and signal propagation constraints, BIUs are generally incapable of performing bus transactions at system clock frequency. For this reason and because some devices coupled to the shared system bus may be incapable of operating at higher frequencies, BIUs are typically "clocked" by a functional signal having a frequency determined by the slowest device coupled to the shared system bus and the frequency range supported by the shared system bus. The frequency of the functional signal is typically lower than the system clock frequency by a fixed ratio, for example, 4:1. This disparity between system clock frequency and BIU functional signal frequency results in unnecessary communication latency in cases in which not all of the devices coupled to the system bus are internally constrained to operate at the common BIU functional signal frequency.
As should thus be apparent, it would be desirable to provide a method and system for bus communication that reduce communication latency by permitting communication circuitry within at least some devices coupled to a shared bus to operate at a relatively higher frequency. In addition, it would be desirable for the method and system for bus communication to permit the operating frequency of the BIU of each device to be individually controlled.